Resistance spot welding is a joining process that is used in many manufacturing processes for making automotive vehicle bodies and other vehicle members. For example, it is used for welding sheet metal inner and outer closure panels (like doors, decklids, liftgates, and hoods) to one another by a series of spot welds at suitable locations on the workpieces. The sheet metal material may be a steel alloy, a galvanized steel, an aluminum alloy, a magnesium alloy, or the like. Assemblies of such workpieces are successively brought to a welding cell (or station) where spot welds are made by one or more pairs of opposing, water-cooled, high conductivity, copper alloy electrodes carried by a welding apparatus. The welding apparatus may be robotic and controlled to clamp and press facing spot welding electrodes against opposite sides of the workpieces and deliver a momentary welding current through the electrodes and workpieces to form a weld between facing surfaces of the metal pieces. The welding apparatus opens the electrodes and advances them (or the workpieces) progressively to make a succession of such welds.
The electrodes are typically round cylinders with one end (a shank end) held in the welding apparatus while the other end presents a weld face that is pressed into electrical contact with a surface of a workpiece. The electrodes are held, generally axially aligned, with their weld faces in opposing, facing relationship. These faces are intended to contact surfaces of one or more metal workpieces and produce a suitable weld nugget.
Electrode faces for spot welding steel have been formed with a spherical domed shape which may be generally concentric with the cylindrical axis of the round electrode body. The domed shape may have been machined with a flat for contacting a steel surface. But these weld faces leave a sharp imprint on the steel surface that can have excessive indentation and/or an unsightly, uneven angle with the workpiece surface. Such an electrode shape is prone to causing sheet deformation around the weld that is unattractive. Also, metal expulsion from the sheet surface can lead to undesirable whiskers or fingers of metal protruding from the sheet surface.
Three co-pending U.S. patent applications, assigned to the assignee of this invention, disclose welding electrodes that form high quality spot welds in metal workpieces. In addition to forming high quality spot welds in steel workpieces, galvanized steel workpieces, aluminum alloy workpieces, or magnesium workpieces, these electrodes form a recognizable image, an attractive image, at the weld site. Viewers of such welded articles have considered these images to have high perceived quality; that is they have a visual appearance which is interpreted as indicating high quality. These applications are No. 11/536,001 (Pub. No. US 2008/0078749), filed Sep. 28, 2006 and titled “Welding Electrode with Contoured Face”; No. 12/251,636, filed Oct. 15, 2008 and titled “Weld Electrode for Attractive Weld Appearance”; and No. 12/356,613, filed Jan. 21, 2009 and titled “Weld Electrode for Attractive Weld Appearance.” These applications disclose the use of protrusions or intrusions in the round (plan view) shaped electrode face. When the shaped end of the electrode engages the workpiece and current flow starts, the protrusions and/or intrusion shapes on the face form complementary (reversed) visible and recognizable weld site images in the weld-heat softened surface of at least one sheet contacted by the electrodes. These images are machined or otherwise formed in the face of one or both of the co-acting copper alloy electrodes. Sometimes the images are in the form of elevated or depressed rings or other geometric shapes in the surface of the electrode face that are concentric with the center of the weld face and commonly concentric with the axis of the electrode. Other visible images may be in the form of letters or icons that are not circular or, if circular, they are not centered on the axis of the round weld face. Preferably such images are formed at weld sites in visible surfaces of articles of manufacture, such as automotive vehicle body surfaces.
This disclosure advances the use of such electrodes by facilitating the shaping or forming of initial electrode weld faces (the workpiece contacting surfaces of the electrodes) and their redressing after welding operations have eroded weld face images.